Plastic liquid crystal display device and method for manufacturing the same

ABSTRACT

A plastic liquid crystal display device and a fabrication method thereof. A plastic substrate having a plurality of bumps on at least one surface thereof is integrally molded. A glass transition temperature (T g ) of the plastic substrate is greater than 150° C. A melt flow index (MFI) of the plastic substrate is greater than 2. A conformal reflective film on the plastic substrate with the bumps is formed. An insulating substrate opposite the plastic plate is provided. A transparent electrode is formed on an inner surface of the insulating substrate. A liquid crystal layer is inserted between the plastic substrate and the insulating substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a plastic liquid crystal displaydevice. More particularly, the invention relates to a plastic liquidcrystal display having a reflector with bumps, and a fabrication methodthereof.

2. Description of the Related Art

A reflective liquid crystal display does not require a backlight moduleas a light source, since it is so configured that an external incidentlight is reflected by a reflector plate provided inside the liquidcrystal display, and the reflected light is utilized as a light source.This has been considered to be an effective means of reducing consumedelectric power and providing thinner and brighter displays. Thus,reflective liquid crystal displays are widely used for portable devices.

Conventionally, in order to enhance reflectivity, a reflector with bumpsis utilized in the reflective liquid crystal display. For example, inU.S. Pat. No. 5,204,765, Mitsui et al discloses a reflector with anumber of convex portions (or bumps). The reflector with bumps caneffectively control the reflective properties of the reflector toprovide a bright screen image.

FIGS. 1A˜1C are schematic illustrations of the different steps on themanufacture of a conventional reflector. In FIG. 1A, an insulation layer120, such as a photosensitive resist layer, is formed on a glasssubstrate 110 by coating. In FIG. 1B, using photolithography, theinsulation layer 120 is partially etched to provide the surface of theinsulation layer 120 with a plurality of bumps 130. In FIG. 1C, areflective film 140 is conformally formed on the insulation layer 120having bumps 130 by deposition, and the conventional reflector is thusobtained. However, the manufacture of the conventional reflector isalways undergoing coating, photolithography, and etching, therebycomplicating fabrication and increasing manufacturing costs.

In U.S. Pat. No. 4,456,336, Chung et al discloses a glass substrate withmicro-lenticular surface fabricated by a peening action, and areflective film formed on the glass substrate to obtain a reflector.However, the profile of the micro-lenticular surface fabricated bypeening is difficult to control, thereby affecting the reflectiveproperties of the reflector.

In addition, the conventional reflector includes a glass substrate,thereby hindering brightening of the display.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method formanufacturing a plastic liquid crystal display device.

Another object of the present invention is to provide a plastic liquidcrystal display having a reflector with bumps.

In order to achieve these objects, a method for manufacturing a plasticliquid crystal display device is provided. Also, the structure of thereflective liquid crystal display device is provided. A plasticsubstrate having a plurality of bumps on at least one surface thereof isintegrally molded. A glass transition temperature (T_(g)) of the plasticsubstrate is greater than 150° C. A melt flow index (MFI) of the plasticsubstrate is greater than 2. A conformal reflective film on the plasticsubstrate with the bumps is formed. An insulating substrate opposite theplastic plate is provided. A transparent electrode is formed on an innersurface of the insulating substrate. A liquid crystal layer is insertedbetween the plastic substrate and the insulating substrate. In addition,the material of the plastic substrate can be PC (polycarbonate), PEN(polyethylenenaphthalate), PSF (polysulfone), PES (polyethersulfone),PAR (polyarylate), COP (cyclo olefin polymer), COC (cyclo olefincopolymer), PNB (polynorbornene), PI (polyimide), PEI (polyetherimide),PPS (polyphenylenesulfide), PEEK (polyetheretherketone) or epoxy.

The present invention improves on the prior art in that the plasticsubstrate with bumps is integrally molded and a reflective film isconformally formed on the plastic substrate with bumps. Moreover, theT_(g) of the plastic substrate is greater than 150° C. and the MFI ofthe plastic substrate is greater than 2. Thus, the invention cansimplify the conventional manufacturing process, thereby increasingthroughput and ameliorating the disadvantages of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading thesubsequent detailed description in conjunction with the examples andreferences made to the accompanying drawings, wherein:

FIGS. 1A˜1C are schematic illustrations of the different steps for themanufacture of the conventional reflector;

FIGS. 2A˜2D are sectional views according to an embodiment of thepresent invention; and

FIG. 3 is a sectional view showing the application of the presentinvention to a reflective plastic liquid crystal display device.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method of forming a reflector suitablefor fabricating plastic liquid crystal display (LCD) products, such asreflective plastic LCD and transflective plastic LCD. Hereinafter, as ademonstrative example, the method of forming a reflector is applied tothe formation of a reflective plastic LCD.

FIGS. 2A˜2D are sectional views according to an embodiment of thepresent invention, which represent the different steps of the method forthe manufacture of a reflector.

In FIG. 2A, an insulating layer (not shown) such as a photoresist layer(or photosensitive resin layer) is coated on a glass plate 210. Then,using photolithography, the insulating layer is partially etched back toform an insulating layer 230 having a plurality of bumps 220 on theglass plate 210. Thus, a mother die 240, including the glass plate 210and the insulating layer 230, is obtained. The bumps 220 can be anydesired shape, such as cylindrical, slanted, or others. It should benoted that the bumps 220 can be continuous or discontinuous. In order tosimplify the illustration, the pattern of continuous bumps 220 is shownin FIGS. 2A˜2D and FIG. 3, but does not limit the present invention.

In FIG. 2B, a metal mold 250 (also referred as to a master matrix) isformed on the mother die 240 by, for example, electroplating orelectroforming/electrotyping, and then the metal mold 250 and the motherdie 240 are separated. Thus, a metal mold 250 having an opposite(negative) profile of the bumps 220 is obtained.

In FIG. 2C, using hot pressing, the metal mold 250 is impressed into aplastic substrate 260 under optimal pressure P and a raised temperature.Thus, a plastic substrate 260 having bumps 270 on at least one surfacethereof is obtained. That is, the plastic substrate 260 having bumps 270is integrally molded and can be mass produced.

It should be noted that the plastic substrate 260 of the presentinvention has heat-resistant, chemical-resistant, and non-deformingreproducible properties. That is, the glass transition temperature(T_(g)) of the plastic substrate 260 is preferably greater than 150° C.Moreover, depending on the requirements of different type displayfabrication, the plastic substrate 260's glass transition temperaturecan be greater than 170° C., 180° C., 220° C. or 250° C. Also, the meltflow index (MFI) of the plastic substrate is preferably greater than 2.Also, depending on the requirements of different type displayfabrication, the plastic substrate 260's melt flow index can be greaterthan 4, 6, 10 or 25. The plastic substrate 260 is transparent or opaque.The material of the plastic substrate 260 can be PC (polycarbonate), PEN(polyethylenenaphthalate), PSF (polysulfone), PES (polyethersulfone),PAR (polyarylate), COP (cyclo olefin polymer), COC (cyclo olefincopolymer), PNB (polynorbornene), PI (polyimide), PEI (polyetherimide),PPS (polyphenylenesulfide), PEEK (polyetheretherketone) or epoxy.Preferably, the material of the plastic substrate 260 is PC, PEN, PSF,PES, PAR, COP, COC, PNB, or PEI. More preferred materials are COC, COPand PNB. Here, the glass transition temperature (T_(g)) of part of theabove plastic materials is shown as Table 1. TABLE 1 Material PC PAR PESCOP COC T_(g) (° C.) 145-195 215 225 100-170 80-330

Generally, the higher the glass transition temperature (T_(g)) of theplastic material, the better the heat resistance. In this embodiment,concerning heatproof requirements, the plastic materials whose glasstransition temperature (T_(g)) is greater than 150° C., 170° C., 180°C., 220° C. or 250° C. are employed.

Generally, the higher the melt flow index (MFI) of the plastic material,the better the flow properties during melting, thereby enabling theplastic substrate with micro-bumps to be precisely molded. The measureof the melt flow index (MFI) is according to, for example, ASTM 1238standard, ISO 1133 standard, or performance under thermal deformationtemperature plus 115° C. for heating temperature and 2.16 kg forloading, and then measuring the weight of the plastic material squeezedout from a tester for 10 minutes. In this embodiment, concerning theprecise reproduction of molding, plastic materials whose melt flow index(MFI) is greater than 2, 4, 6, 10 or 25 are employed.

In FIG. 2D, a conformal reflective film 280 is formed on the plasticsubstrate 260 with the bumps 270, and thus a reflector including theplastic substrate 260 and the reflective film 280 is obtained. Thereflective film 280 can be a metal film, such as an aluminum (Al) filmor a silver (Ag) film, formed by deposition or sputtering. It should benoted that the reflective film 280 can include a transflective function,such as a transflective or semitransparent film. That is, the presentinvention is also suitable for the transflective LCD process.

As a demonstrative experiment, the reflective film 280 is respectivelyformed on the mother die 240 with the bumps 220 and the plasticsubstrate 260 with the bumps 270 (made of COC whose T_(g) is 180° C. andMFI is 6). Then, the scatter distribution of the reflective lightaccording to the above is detected, and the scatter distribution of bothis almost the same is founded. Thus, it is identified that the profile(or pattern) of the bumps 270 of the plastic substrate 260 manufacturedby the present method is almost the same as the bumps 220 of the motherdie 240.

Although the hot pressing procedure is used in this example to form anintegrally molded plastic substrate 260, other molding methods can beused, such as injection molding, extrusion embossing, monomerpolymerization, solution forming and teeming. Nevertheless, a heatingmolding method, such as hot pressing, injection molding, or extrusionembossing, is preferred. It should be noted that because the plasticsubstrate 260 has a heat-resistant, chemical-resistant, andnon-deforming reproducible properties, the profile (or pattern) of thebumps 270 of the plastic substrate 260 is almost the same as the bumps220 of the mother die 240 after molding. Thus, the inventive method iswell suited for fabricating plastic reflective display products.

Next, referring to FIG. 3, the application of the present invention to areflective liquid crystal display device is provided.

In FIG. 3, an alignment film 310 is formed on the reflective film 280.An insulating substrate 340 opposite the plastic substrate 260 isprovided, wherein the insulating substrate 340 can be a glass plate or aplastic plate. A transparent electrode 330, such as an ITO (indium tinoxide) film or an IZO (indium zinc oxide) film, is formed on the innerside of the insulating substrate 340. Moreover, another alignment film315 is formed on the inner side of the transparent electrode 330.

In FIG. 3, a liquid crystal layer 320 is inserted between the plasticsubstrate 260 and the insulating substrate 340. Thus, a reflectiveplastic liquid crystal display device having the integrally moldedplastic substrate 260 is obtained. In order to avoid obscuring aspectsof the present invention, the details of the RLCD process are notfurther described.

The present invention provides a method of forming a reflective plasticliquid crystal display device having an integrally molded plasticsubstrate with bumps, and the structure thereof. Moreover, since theT_(g) of the plastic substrate is greater than 150° C. and the MFI ofthe plastic substrate is greater than 2, the plastic substrate has atleast heat-resistant and non-deforming reproducible properties. Thus,the invention can simplify the conventional manufacturing process,thereby increasing throughput, decreasing the production cost andameliorating the disadvantages of the prior art

Finally, while the invention has been described by way of example and interms of the above, it is to be understood that the invention is notlimited to the disclosed embodiments. On the contrary, it is intended tocover various modifications and similar arrangements as would beapparent to those skilled in the art. Therefore, the scope of theappended claims should be accorded the broadest interpretation so as toencompass all such modifications and similar arrangements.

1-13. (canceled)
 14. A plastic liquid crystal display device,comprising: a plastic substrate having a plurality of bumps on at leastone surface thereof, wherein the plastic substrate with the bumps isintegrally molded and has heat-resistant and non-deforming reproducibleproperties; a reflective film formed on the plastic substrate with thebumps; a insulating substrate opposite the plastic substrate; atransparent electrode formed on an inner surface of the insulatingsubstrate; and a liquid crystal layer inserted between the plasticsubstrate and the insulating substrate.
 15. The plastic liquid crystaldisplay device according to claim 14, wherein a glass transitiontemperature (Tg) of the plastic substrate is greater than 150° C. 16.The plastic liquid crystal display device according to claim 14, whereina melt flow index (MFI) of the plastic substrate is greater than
 2. 17.The plastic liquid crystal display device according to claim 14, whereinthe plastic substrate is a PC (polycarbonate), PEN(polyethylenenaphthalate), PSF (polysulfone), PES (polyethersulfone),PAR (polyarylate), COP (cyclo olefin polymer), COC (cyclo olefincopolymer), PNB (polynorbornene), PI (polyimide), PEI (polyetherimide),PPS (polyphenylenesulfide), PEEK (polyetheretherketone) or epoxysubstrate.
 18. The plastic liquid crystal display device according toclaim 14, wherein the reflective film is an aluminum (Al) or silver (Ag)film.
 19. The plastic liquid crystal display device according to claim14, wherein the insulating substrate is a glass or plastic substrate.20. The plastic liquid crystal display device according to claim 14,wherein the transparent electrode is an ITO (indium tin oxide) or IZO(indium zinc oxide) electrode.